Ion Exchange Membranes: Constructing and Tuning Ion Transport Channels

Abstract Ion exchange membranes (IEMs) that can selectively transport ions are crucial to a variety of applications, such as ion extraction/separation, fuel cells, redox flow batteries, and water electrolysis. IEM performance, in terms of membrane permeability/conductivity and selectivity, relies heavily on the formation of effective ion transport channels within the membranes, and there exists a tradeoff between permeability/conductivity and selectivity, which obstructs the development and widespread adoption of IEM‐based processes. To overcome this tradeoff and to advance IEM‐related applications, extensive research efforts are devoted to the construction and tuning of ion transport channels, and various strategies are proposed. These strategies mainly include 1) inducing microphase separation by properly regulating the polymer architecture, 2) introducing a third phase/region for ion transfer, 3) realizing a high free volume with polyrotaxanes or polymers with sterically bulky groups, and 4) constructing ion transport channels with nanoporous materials. These strategies are outlined and summarized in this review. Perspectives and future research directions are also discussed.